One form of integrated circuit package, called gull-wing because of the shape of the leads, is a popular surface mount design that is easy to solder and inspect. But since the leads are thin and extend away from the body of the package the leads are easily bent or broken. It is important to protect these leads especially for expensive large scale integration (LSI) chips. LSI is herein used as a generally descriptive term for any of the larger packages with large ICs, multiple hybrid ICs, or any other composite type construction. LSI is not limited to a narrow definition.
IC manufacturers routinely package these ICs in trays or carriers that protect the IC pack from static charge and physical harm during routine handling and shipping. It is important to protect the fragile leads. These trays often provide guides that substantially enclose the leads. Such guides prevent the test/burn-in or other use of the ICs while still packaged.
IC end users and test houses prefer, to reduce handling of the chip (herein defined as the packaged IC), to use the trays in which the chips are shipped. ICs often go through a series of handling operations that are a source of failure for such ICs; the ICs are: removed from the shipping carriers, placed in programming/test/burn-in fixtures, programmed/tested, repackaged for stocking or subsequent shipping, and then placed in another socket/fixture or soldered to a PCB for use. This handling (or mishandling) is a source of harm to the ICs.
Sockets are routinely used on PC boards to allow the IC to be changed or interconnections modified as the circuitry and programming are being debugged or upgraded. But in production, sockets are a source of failure, usually due to mechanical problems of alignment, unreliable electrical contacts and sometimes added capacitance and inductance associated with the socket itself. In addition there is an added cost of the socket. Sockets are often bulky with high profiles obviating their use in closely stacked board assemblies. These negatives are balanced by the ability of replacing or reprogramming the chip without damaging the PC board. This is important since LSI chips and completed PC boards are expensive, and replacing a soldered on chip without damaging the board or the replacement chip is a skill that is not routinely done nor recommended in production or even in development environments.
An object of this invention is to provide an IC carrier/socket system wherein the IC package and its gull wing leads are protected during routine inspection, test/burn-in, programming, reprogramming and use.
It is a another object to provide an IC carrier/socket system wherein the IC is placed in the protective carrier that may be placed in a programming/test/burn-in socket for programming/test/burn-in of the IC, and then the carrier (and IC) may be placed in an SMT socket soldered onto a PC board for system debugging.
It is a further object to provide a carrier/socket system wherein the SMT socket may be used on production PC boards thereby allowing field replacement.
Another object of this invention is to provide an SMT/production socket with a contact layout footprint that matches the gull-wing pad footprint of the IC.
It is another object of this invention to provide a carrier/socket system wherein the carrier/socket has minimum impact on the electrical performance of the IC.